Firefighters dodged exploding 55-gallon chemical drums and battled heat and poisonous fumes for more than three hours before the fire at the Drexel Chemical Co. was brought under control.

At the height of the fire, police and fire dispatchers broadcast warnings that the smoke cloud contained nerve gas, and police, firefighters and reporters at the scene were warned stay out of the smoke The Coast Guard blocked river traffic on the nearby Mississippi for a time as the chemical cloud moved westward.

Thirty-three persons were treated for possible chemical poisoning, but none was admitted, a hospital spokeswoman said. Another 25 persons were treated for burns or smoke inhalation, including the three plant workers and six firefighters. The firefighters' injuries were not considered serious, officials said.

Drexel President Robert Shockey said damage to his company could reach $4 million, and lost sales might be as much as $8 million. CAPTION: Picture, Clouds of toxic pesticide billow from Memphis plant.